An endoprosthesis or intraluminal prosthesis is a medical device used in the treatment of diseased bodily lumens. One type of endoprosthesis used in the repair and/or treatment of diseases in various body vessels is a stent. A stent is a generally longitudinal tubular device formed of biocompatible material which is useful to open and support various lumens in the body. For example, stents may be used in the vascular system, urogenital tract, esophageal tract, tracheal/bronchial tubes and bile duct, as well as in a variety of other applications in the body. These devices are implanted within the vessel to open and/or reinforce collapsing or partially occluded sections of the lumen.
Stents generally include an open flexible configuration. This configuration allows the stent to be inserted through curved vessels. Furthermore, this configuration allows the stent to be configured in a radially compressed state for intraluminal catheter implantation. Once properly positioned adjacent the damaged vessel, the stent is radially expanded so as to support and reinforce the vessel. Radial expansion of the stent may be accomplished by inflation of a balloon attached to the catheter or the stent may be of the self-expanding variety which will radially expand once deployed. Tubular shaped structures, which have been used as intraluminal vascular stents, have included helically wound coils which may have undulations or zig-zags therein, slotted stents, ring stents, braided stents and open mesh wire stents. Super-elastic materials and metallic shape memory materials have also been used to form stents.
A stent may be delivered to a specific location within a body lumen by a delivery system. The delivery system includes an elongate inner structure on which an endoprosthesis holder is supported. The elongate inner structure may be cylindrical. The endoprosthesis holder may be tubular and supported on the elongate inner structure in coaxial relation therewith. A tubular stent is supported on the endoprosthesis holder. If the endoprosthesis holder is tubular, the stent is supported in coaxial relation therewith. A tubular sheath covers the stent in coaxial relation therewith and with the elongate inner structure. The endoprosthesis holder is fixed to the elongate inner structure to prevent axial displacement of the endoprosthesis holder relative to the elongate inner structure. The endoprosthesis holder engages the stent to prevent axial displacement of the stent relative to the endoprosthesis holder. This retention of the stent by the endoprosthesis holder maintains the axial position of the stent relative to the endoprosthesis holder and elongate inner structure when the sheath is axially displaced relative to the elongate inner structure and endoprosthesis holder. Without the retention of the stent provided by the endoprosthesis holder, axial displacement of the sheath relative to the elongate inner structure may cause associated axial displacement of the stent as a result of frictional contact between the sheath and stent.
The retention of the stent by the endoprosthesis holder is beneficial during deployment of the stent by providing for the longitudinal position of the stent within the bodily lumen to be maintained during relative axial displacement of the sheath. The longitudinal position of the stent within the bodily lumen is typically significant. The maintenance of the longitudinal position of the stent relative to the elongate inner structure may be particularly difficult during reconstrainment. The sheath may be longitudinally retracted relative to the elongate inner structure such that a distal axial portion of the stent is exposed by the sheath and a proximal axial portion of the stent remains covered by the sheath. Reconstrainment refers to the forward axial displacement of the sheath relative to the elongate inner structure such that the axial distal portion of the stent which was uncovered by the longitudinal retraction of the sheath is recovered partially or completely by the sheath. The forward axial displacement of the sheath may cause forward longitudinal displacement of the stent relative to the elongate inner structure and, typically, the bodily lumen as a result of contact between the sheath and stent. Accordingly, the stent may be carried by the sheath. Limiting or completely preventing such forward displacement of the stent relative to the elongate inner structure and bodily lumen is typically advantageous.
Stents frequently are required to be delivered through bodily lumens which are curved and tortuous. Typically, it is desirable for the endoprosthesis holder, stent, sheath, and elongate inner structure to have sufficient flexibility to conform to the curved and tortuous sections of the bodily lumen during delivery of the stent therethrough. Such conformance by the endoprosthesis holder normally requires the endoprosthesis holder to be flexible to resist kinking thereof. Also, it is desirable for the endoprosthesis holder to be torsionally stiff.